Rangeland Plant Ecophysiology Wednesday, September 16, 2009 Crassulacean Acid Metabolism CAM physiology, biochemistry, anatomy Ecology of CAM plants Phylogenetics and biogeographic distribution CAM idling CAM cycling Facultative CAM Aquatic CAM plants?

ATP ADP C4 photosynthetic pathway

8.14 Crassulacean acid metabolism (CAM) (Part 1) 1. Starch is degraded at night to form PEP, a 3-carbon compound. 2. PEP combines with HCO 3 - (hydrated CO 2 from atm). Reaction is catalyzed by PEP-carboxylase. 3. The 4-carbon acid (OAA) is converted to Malate where it is actively (ATP) pumped into vacuole and stored as malic acid. 4. Acidity (and malic acid concentration) of vacuole builds up at night as reaction proceeds.

8.14 Crassulacean acid metabolism (CAM) (Part 2) 1. The next morning, stomates close, and malic acid is transported out of vacuole and decarboxylated to Pyruvate. 2. CO 2 concentration builds inside tissues where it diffuses to chloroplasts to be assimilated by Rubisco in Calvin cycle. 3. Some of the starch that is built up during day is converted at night to PEP.

Taiz and Zeiger, Figure 9.24 – CAM gas exchange

CAM is an adaptation to drought! Epiphytes in Trinidad

Amount of water loss per amount of CO 2 gain (g H 2 O / g CO 2 ) Water-use efficiency (WUE)

Fick’s law (Don’t forget it!)

Facultative CAM Example: Ice plant (Mesembryanthum crystallinum)

Another facultative CAM Agave deserti of the Sonoran desert

Some submerged aquatic plants (e.g., Isoetes) have evolved the CAM photosynthetic pathway. WHY?

Terms to know: CAM – Crassulacean Acid Metabolism photosynthetic pathway malic acid vacuole succulence Water-use efficiency in CAM plants CAM idling CAM cycling facultative CAM aquatic CAM plants